The long-term goal of this project is to develop more effective immunotherapy for cancer. Each year more than 500,000 deaths from cancer occur in the United States. Conventional chemotherapy is toxic and of limited efficacy for many tumor types. Preclinical animal models indicate that cytokines such as interleukin-12 (IL-12) can promote effective antitumor immune responses in vivo. In many models production of interferon-gamma (IFN-gamma) is required for successful immunotherapy of cancer. STAT4 is critical for IL-12-induced IFN-gamma production and the development of Th1-type immune responses. Cancer patients who have undergone high-dose chemotherapy and autologous hematopoietic stem cell transplantation exhibit defective IFN-gamma production during IL-12 therapy. This defective IFN-gamma response is due to a profound and selective deficiency of STAT4 in lymphocytes of cancer patients after transplantation. The objectives of this proposal are to determine the mechanisms of STAT4 deficiency in cancer patients and to develop clinically feasible approaches to circumvent this deficiency and promote IFN-gamma production during cancer immunotherapy. There are three Specific Aims: 1) To determine the molecular mechanisms of STAT4 deficiency and develop approaches to enhance STAT4 expression after autologous transplantation;2) To characterize and develop methods to enhance STAT4-independent mechanisms of IFN-gamma production;3) To evaluate disease-related and treatment-related contributions to STAT4 deficiency in cancer patients. The results of studies in this proposal will permit the development of rational approaches to enhance STAT4 expression and recruit STAT4-independent pathways of IFN-gamma production during cancer immunotherapy. Understanding the clinical causes of STAT4 deficiency will also facilitate the optimal design of immunotherapy for cancer. Relevance: The purpose of this research project is to determine why STAT4, an important component of the immune system, is defective in patients with cancer. Understanding the causes of this deficiency will allow the development of strategies to correct it and/or find ways around it. This is essential for clinical efforts to stimulate the immune system to fight cancer.